This research investigates respiratory control in both normal subjects and in patients with respiratory system abnormalities by examining aspects of respiratory muscle function under various states and with several respiratory stimuli. In the first of three phases of the study the segmental muscle reflexes are examined using the electromyographic responses of the important respiratory muscles to sudden respiratory loads (airway resistance or occlusion) and to the release of resistive loads. The second phase of the study combines the techniques of sleep research and respiratory physiology to investigate the relationships between the states of sleep (quiet vs R.E.M.) and respiratory control. Using both EMG's of respiratory muscles and magnetometer measurements of thoracoabdominal motion, patterns of breathing, reflex responses of loading and responses to hypercapnia will be assessed in both normals, respiratory disease patients and patients with sleep apnea syndrome while awake and in both quiet and R.E.M. sleep. The third phase of the program addresses the problem of respiratory muscle fatigue and its relationship to respiratory disability and failure. Two indicators of respiratory muscle fatigue, respiratory muscle incoordination and frequency shifts in respiratory muscle electromyograms, will be examined and compared and evaluated as early indices of fatigue and failure. Studies will be done in three subject groups, normal subjects, high (C1-2) quadriplegics with electrophrenic pacers and patients in actual, impending or recovering respiratory failure. Effects of lung volume changes (passively achieved) will be evaluated, and the quadriplegics with phrenic pacers may allow myogenic and neurogenic factors to be evaluated separately as to their effects upon the electromyographic frequency spectra of respiratory muscles.